......engram to refer to the neural representation of a memory.
It seemed that the memory loss was related more to the size of the lesion than to its placement in the cortex.
He used a behavioral task that could be solved in different ways.
As the lesions got bigger, more processes were distrupted, leaving the animal with fewer options for solving the problem.
H.M could recall many of the events of his earlier life, especially those that occured up to several years before the surgery, he was unable to form memories for experiences that occured after the surgery, hewas unable to form memories for a few seconds (he had short-term memories), but he couldn't convert this information into long-term memories. He failed to recognize himself in a mirror, for example, but did recognize himself from... (查看原文)
Procedual memory was therefore later renamed with more neutral designation: nondeclaractive memory. The term explicit and implicit memory, suggested by Dan Schacter, essentially refer to the same memory processes as declarative and nondeclarative memory.
Outputs of each of the cortical areas then converge in the rhinal cortical areas, also known as the parahippocampal region, which integrates information from different sensory modalities before shipping it to the hippocampus proper. (查看原文)
In this way, cortical areas involved in processing a stimulus can, as we will soon see, also participate in the long term storage of memories about that stimulus.
Convergence zones also allow mental representations to go beyond perceptions and to become conceptions - they make possible abstract representation s that are independent of the concrete stimulus. (查看原文)
There are basically two kinds of amnesia: one is an inability to remember things that happenred before the surgery or brain injury (called retrograge amnesia), and the other is an inability to form new memories (called anterograde amnesia). While we' ve focused so far on anterograde amnesia, both forms are present in patient with damage to the temporal lobe. Interestingly, the degree of retrograde amnesia is graded over time - memory is worse for events right before the surgery than for earlier ones.
The graded effect of retrograde amnesia is now believed to occur because the role of hippocampus changes over time - the hippocampus is needed for memory storage initially, butits role decreases as time goes by. (查看原文)
But with the interleaved learning, where the reoresentaion is built up slowly over many repetitions, the network gradually refines the representation...... (查看原文)
Each reinstatement changes cortical synapses a little. Because the reinstatement depend on the hippocampus, damage to the hippocampus affects recent memories, but not old ones that have already been consolidated in the cortex. (查看原文)
Subsequently, when the rats went to sleep, the neural patterns seemed to be repeated in the hippocampus, as if the rats were dreaming about the places they had explored. (查看原文)
However, with time, the memory trace comes to involve more and more brain regions, especially cortical regions, so that damage to one area, like hippocampus, fails to produce a deficit, since the other areas compensate.
With time, hippocampal activity decreased and came to be unrelated to memory performance, while cortical activity increased and came to be related to the memory performance. (查看原文)
He argued that episodic memories are about personal experiences (things happened to you at a particular time and place), while semantic memories are about facts (things you come to know, but have not necessarily experienced)......Tulving suggested that episodic memory, which requires conscious recollection of the time and place of some personal experience, is particular characteristic of humans, whereas semantic memories, being the single storage of a fact rather than a personal experience, is within tha capacity of many animals. (查看原文)
One is that episodic memory, while poor, is still present in the children, and that even a littlespisodic memory capacity may be sufficient to support a gooddeal of semantic knowledge......but episodic deficit may be more readily detect. (查看原文)
It turned out, though, that the effects of the lesions were not due to damage to the amygdala or hippocampus, but to damage of surrounding parahippocampal region. (查看原文)
In sum it seems that the parahippocampal areas and hippocampus make unique contributions, and the delayed nonmatch to sample task reflects the parahippocampal more than the hippocampal contribution. (查看原文)
......different cells in the hippocampus are active at different locations.
One of the few tasks that hippocampal leision seemed to impair with any consistency was maze learning, a task that is often solved by spatial cues. (查看原文)
Specifically, declarative memories are relational. Thus, activation of a declarative memories can be activated independent of the context in which they were established, and by stimuli other than those that were initially involved in the learning. (查看原文)
In this theory, the original elements, though, are lost, having been formed into conjunctions, while in the relational theory, the elements remain discrete and the hippocampus links them together. (查看原文)
The hippocampus learns conjunctions naturally and rapidly. When the hippocampus is damaged, the neocortex can be forced, through extensive training, to also learn conjunctions, but normally it does not do so. (查看原文)
作者: Joseph LeDoux, [美国] 约瑟夫·勒杜 副标题: How Our Brains Become Who We Are isbn: 0142001783 书名: Synaptic Self 页数: 416 定价: USD 18.00 出版社: Penguin Books 出版年: 2003-1-28 装帧: Paperback
